The present invention relates to sensors for sensing conditions in ambient and controlled environments. The invention is described with particular reference to sensors for sensing electrical fields, magnetic fields, temperature, pH, humidity, and other conditions which have a differential effect on materials.
Heretofore, fiber optic sensors have been utilized to sense a variety of conditions, such as motion. In one prior art motion detector, a pair of light sensors were disposed behind a pair of slits. A lever arm carried an optical fiber to a point closely adjacent and generally between the two slits such that each sensor sensed generally the same amount of light. Under acceleration, the lever arm would bend in proportion to the acceleration moving the lever arm toward one slit and away from the other. This motion changed the relative amount of light sensed by each sensor generally in proportion to the acceleration forces. By comparing the sensor outputs with each other, the device could be calibrated to provide an indication of acceleration.
Other acceleration monitors alter the light transmissive properties of an optical fiber in accordance with the amount of acceleration. The optical fibers were placed relative to a mass such that the mass deformed the optical fiber. For example in some sensors, the mass stretched the optical fiber in accordance with acceleration. In other applications, the mass bent or flexed the optical fiber sufficiently to alter light transmission in accordance with acceleration.
Analogously, fiber optic chemical and biological sensors have been designed in which the light transmissive properties of the optical fiber are altered by the presence of certain chemical substances. For example, the amount of light transmitted through the core of an optical fiber was altered as the cladding layer absorbed one or more selected chemical fluids. Analogously, a cladding was selected whose properties change in response to electromagnetic, electrical, or sonic energy.
As another example, two optical fibers have been arranged end to end with a gap therebetween. A structure, such as a grating or a shutter, which moves in response to a sensed condition, was positioned in the gap. For example, the shutter snapped between blocking and retracted positions in response to a sensed condition. Alternately, a multiple grating moved in proportion to a sensed condition, such a pressure, to adjust the degree of light transmission analogously.
The prior art sensors, particularly those that mechanically deform the optical fiber to alter the light passage therethrough, tend to be relatively expensive to manufacture. The small sizes and critical tolerances compound manufacturing difficulties.
The present invention contemplates a new and improved sensor that is simple to manufacture and amenable to automated manufacturing procedures.